The disclosure generally relates to a transmission line driver circuit and, more particularly, to a transmission line driver circuit for automatically calibrating impedance matching.
In the ideal situation, an output circuit and an input circuit should operate under an impedance matching condition to efficiently deliver signals and energy. That is, the internal resistance of the output circuit should be identical to the input resistance of the output circuit, and the output impedance of the output circuit should be identical to the impedance of the input circuit (also refers to the load). A maximum transmission power can be achieved when the output circuit and the input circuit reach the impedance matching condition. On the contrary, if the output circuit and the input circuit cannot reach the impedance matching condition, it is impossible to maximize the transmission power and may also damage the circuits.
For example, when impedance mismatching occurs between the output circuit and the input circuit, it often results in asymmetry in the differential output currents of the output circuit, thereby causing EMI (electromagnetic interference) problems. In addition, the return loss is also increased when impedance mismatching occurs between the output circuit and the input circuit.